12th of July is the date that Billy of Orange beat the Catholics up centuries ago, some members of the Orange Order - a Protestant organisation that doesn’t like Catholics - like to celebrate that by marching through Catholic neighboirhoods singing anti-Catholic songs, some Republicans don’t appreciate that. Violence ensues.
Wow, you love the republican side.
Anyway, for a slightly more balanced account of what happened in Londonderry: the Orange Order marched on the Thursday. A nationalist crowd attempted violence in the city centre but was prevented by the police. That evening and the following day... gangs of nationalists attempt to kill police officers.
I actually only know this from the article you yourself linked:
A Twelfth of July parade passed off peacefully in Derry on Thursday, although police in riot gear separated a group of nationalists from the return parade as it made its way through the Diamond in the city centre.
Attacks began early in the evening and continued into the early hours of Friday morning.
Petrol bombs were thrown towards police Land Rovers and at officers on the ground
it is clear that this is being orchestrated by a more sinister, adult, violent dissident republican element.
All of which seems to suggest that the riot wasn't because the nasty
bogeymen Orangemen riled up the otherwise peaceful republicans. It was because violent republicans wanted to stir up yet more sectarian hate - a sin of which the Loyalist side is by no means innocent either.
I understand the desire to utilise populism and its associated buzzwords in an argument, hector, but please do not try to present it as a definitive and all encompassing account to those who ask for... well, information.
As an aside, I've yet to hear an Orange parade sing sectarian songs. This possibly stems from the fact that I have not seen a contested parade. Largely, however, I suspect that it is because most (possibly all?) are instrumental and lacking the necessary vocal component.